1. Field of the Invention
The invention relates to an illumination technology, and more particularly, to an illumination system having functionalities of an adjustable color temperature and brightness adjustment and a control method thereof.
2. Description of Related Art
Cold color white light lamps or warm color white light lamps are usually chosen as light sources for indoor illumination. Generally speaking, if the cold color white light lamps are chosen, only cold color white light is emitted but the lamps may not be switched to warm color white light. However, if the lamps may be adjusted to warm color white light source in winter and adjusted to cold color white light source in summer, the lamps make people feel warm and cool in terms of visual sense.
Due to such an objective, Taiwan patent No. M314819 provides a “white light emitting diode (LED) illumination unit capable of adjusting brightness/darkness and color temperature (hereinafter referred to be 819' patent)”. The 819' patent mainly utilizes a microcontroller to control two pulse width modulation (PWM) signals with a phase difference of 180 degrees therebetween, under a fixed power mode or a fixed current mode, for respectively modulating a light-up duration ratio of a warm color white light LED array to a cold color white light LED array and adjusting current level so as to adjust color temperatures and brightness/darkness required by a white light LED light source.
However, since the mechanism of respectively modulating the light-up duration ratio of a warm color white light LED array to a cold color white light LED array and adjusting current level proposed by the 891' patent utilizes two PWM signals with the phase difference of 180 degrees, the color temperatures may not be ensured to maintain unchanged when brightness and darkness are adjusted. Besides, suppose maximum power consumptions of the warm color white light LED array and the cold color white light LED array are respectively 50 Watts (W) and a maximum value of the PWM signals with the phase difference of 180 degrees is 100%, the 819' patent is required to utilize a power circuit design and components of high power consumption of 100 W (50 W×100%+50 W×100%), and the cost may be relatively high. In addition, Taiwan patent Nos. 480739, I246207 and Taiwan patent publication Nos. 200841767, 200731044 disclose techniques of adjusting color temperatures and/or brightness by controlling the red (R), green (G), and blue (B) LEDs.